Semiconductor wafer alignment tools

ABSTRACT

In one embodiment, a photomask is provided having a set of alignment pattern openings and circuitry openings formed therethrough. With the photomask, the substrate is first photoexposed through one of the set of alignment pattern openings and the circuitry openings and not the other. After the first exposing, the substrate is second exposed through the other of the openings on the photomask. In another embodiment, a latent image of an alignment pattern is formed and received by a masking layer over a substrate. The position of the latent image of the alignment pattern is inspected relative to an underlying layer of material over the substrate. Alignment is ascertained through inspection of the latent image relative to the underlying layer of material. In another embodiment, an undeveloped photoresist layer is formed over a substrate. The undeveloped photoresist is exposed to processing conditions effective to form an image of an alignment pattern received over the undeveloped photoresist over a wafer scribe area. The image of the alignment pattern received by the undeveloped photoresist is inspected relative to an underlying substrate structure over the scribe area and alignment information is ascertained therefrom. In a preferred embodiment, if an alignment error is detected, the error can be corrected in real time, and the substrate further processed without reapplication of a masking layer or photoresist layer.

This application is a divisional application of U.S. patent applicationSer. No. 09/145,492 6,068,954 6,068,954 Jun. 15, 2000.

TECHNICAL FIELD

This invention relates to semiconductor wafer alignment methods and tosemiconductor wafer alignment tools.

BACKGROUND OF THE INVENTION

Integrated circuits are typically formed through a number of steps whichinclude patterning and etching various features over a substrate. Anecessary requirement imposed on the patterning and etching of substratefeatures is that such features be aligned relative to other features onthe substrate. Failure to achieve adequate alignment can render afabricated device inoperative.

One way of maintaining alignment during a fabrication process, whichoften involves forming multiple layers over a substrate and aligningeach of the layers to one or more other layers, is to use so-calledalignment or registration marks. Alignment or registration marks aretypically provided over a scribe area of a wafer between individual diearea. Alignment or registration marks can be provided on a substratethrough utilization of a mask which contains not only alignment markpatterns, but also integrated circuitry patterns as well. One pastpractice has been to expose the entire mask, including the integratedcircuitry patterns, to lithographic processing, and then inspect thetransferred alignment patterns for alignment. If the alignment patternswere not desirably aligned, the alignment process was repeated byremoving the patterned layer, re-applying and patterning it, and theninspecting for alignment. For example, a layer of photoresist willtypically be formed over a substrate. A mask will be utilized to form apattern over the photoresist, which photoresist is subsequentlydeveloped to provide alignment marks over the substrate, as well asintegrated circuitry patterns. If the alignment marks are not desirablyaligned, the photoresist is removed, reapplied (which can includetime-consuming baking), reexposed, redeveloped and examined formisalignment again. Needless to say, removal, reapplication, reexposure,redevelopment, and reexamination of the photoresist takes preciousproduction time and reduces throughput of the wafers.

This invention arose out of concerns associated with improving themethods through which integrated circuitry devices are formed, and inparticular, with providing improved wafer alignment methods and tools.

SUMMARY OF THE INVENTION

In one embodiment, a photomask is provided having a set of alignmentpattern openings and circuitry openings formed therethrough With thephotomask, the substrate is first photoexposed through one of the set ofalignment pattern openings and the circuitry openings, and not theother. After the first exposing, the substrate is second exposed throughthe other of the openings on the photomask. In another embodiment, alatent image of an alignment pattern is formed and received by a maskinglayer over a substrate. The position of the latent image of thealignment pattern is inspected relative to an underlying layer ofmaterial over the substrate. Alignment is ascertained through inspectionof the latent image relative to the underlying layer of material. Inanother embodiment, an undeveloped photoresist layer is formed over asubstrate. The undeveloped photoresist is exposed to processingconditions effective to form an image of an alignment pattern receivedover the undeveloped photoresist over a wafer scribe area. The image ofthe alignment pattern received by the undeveloped photoresist isinspected relative to an underlying substrate structure over the scribearea and alignment information is ascertained therefrom. In a preferredembodiment, if an alignment error is detected, the error can becorrected in real time, and the substrate further processed withoutreapplication of a masking layer or photoresist layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 shows a top plan view of a mask in accordance with one embodimentof the present invention.

FIG. 2 shows a portion of a substrate having exposed thereon analignment pattern in accordance with one embodiment of the presentinvention.

FIG. 3 shows a portion of a substrate which is processed in accordancewith one embodiment of the present invention.

FIG. 4 is a top plan view of a substrate having an alignment patternexposed thereon in accordance with another embodiment of the invention.

FIG. 5 is a view of a substrate portion which is processed in accordancewith another embodiment of the invention.

FIG. 6 is a high level flow diagram which illustrates one method inaccordance with one embodiment of the present invention.

FIG. 7 is a view of a semiconductor wafer alignment tool in accordancewith one embodiment of the invention.

FIG. 8 is a high level schematic diagram of a semiconductor waferalignment tool.

FIG. 9 is a top plan view of an integrated assembly comprising a mask,in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring to FIG. 1, a portion of a photomask is provided generally at10 and includes a set of alignment pattern openings 12 and areas 14within which integrated circuitry openings defining integrated circuitrypatterns are provided. Alignment pattern openings 12 and integratedcircuitry openings within areas 14 are disposed adjacent one another.Photomask 10 is to be used to transfer openings 12, and integratedcircuitry openings defining integrated circuitry patterns within areas14 onto a substrate as described below.

Referring to FIG. 2, a semiconductor wafer substrate is provided at 16.Substrate 16 comprises die areas 18 within which active devices are tobe disposed, and various dedicated alignment areas or scribe areas 20which are displaced from die areas 18 and within which alignmentprocessing is to take place. The boundaries between areas 18, 20 areshown by a dashed line. Alignment areas or scribe areas 20 containvarious alignment reference marks which are utilized to align variouslayers during processing. In the illustrated example, one such alignmentreference mark is shown at 22 which is disposed within apreviously-provided underlying layer.

In one embodiment, a layer of undeveloped photoresist 24 is formed oversubstrate 16 and exposed to processing conditions effective to form animage of an alignment patter 12 (corresponding to alignment patternopening 12 in FIG. 1) received by the undeveloped photoresist 24 overwafer scribe area 20. Subsequently, the image of alignment pattern 12received by undeveloped photoresist layer 24 is inspected relative to anunderlying substrate structure, which in this example comprisesalignment reference mark 22. Such inspection enables one to ascertainwhether the image of alignment pattern 12 is aligned with the underlyingsubstrate structure. Inspection can take place through visual inspectionor automated inspection using conventional metrology tools, or toolssuch as those described in connection with the invention below. Suchconstitutes an improvement over prior processes which required that thephotoresist be developed prior to inspection for alignment. In thisembodiment, the photoresist is not developed prior to inspection foralignment. This can significantly improve processing time and increasethroughput. In addition, any perceived misalignments can be corrected onthe spot thereby providing for effective real time alignment correction.Specifically, if a misalignment is detected, such can be corrected priorto exposure of unexposed photoresist over other wafer areas, which, in apreferred embodiment comprises exposure to transfer integrated circuitrypatterns into the photoresist.

In another embodiment, a latent image of alignment pattern 12 isreceived by a masking layer, such as photoresist layer 24, oversubstrate 16. A latent image is an image which has been introduced intoan energy sensitive material, e.g. by exposing the material toradiation, and in some cases, baking the material, but which has notbeen developed. Subsequently, the position of the latent image ofalignment pattern 12 is inspected relative to an underlying layer ofmaterial over the substrate. Hence, a determination can be made whetherthe latent image of alignment pattern 12 is aligned within desiredalignment tolerances. In this instance, the underlying layer of materialrelative to which the latent image is inspected contains an alignmentreference mark 22 relative to which the latent image of alignmentpattern 12 is compared. Preferably, a plurality of transferred alignmentimages are formed over the substrate so that alignment inspection cantake place in both X and Y directions. By using a latent image of thealignment pattern, other portions of the masking layer not having thelatent image formed thereon can be preserved for further processing. Forexample, if no misalignment is detected, those other portions of themasking layer can be processed to form integrated circuitry. If amisalignment is detected, the misalignment can be corrected on the spot,with further processing of the other portions of the masking layertaking place to form integrated circuitry.

In another embodiment, layer 24 is exposed to processing conditionsthrough a partially obscured mask effective to form a latent image ofalignment pattern 12 over the substrate. In the illustrated example,portions of mask 10 (FIG. 1) can be blocked, with subsequent processingforming images of only unblocked portions of the mask over thesubstrate. In a preferred mask-blocking embodiment, at least portions ofthe integrated circuitry patterns on the mask, and preferably all of theintegrated circuitry patterns on the mask are blocked. One way ofimplementing a mask-blocking embodiment is shown in FIG. 9 which showsan integrated assembly known as a Reticle Masking Assembly (REMA)comprising a plurality of blades B₁, B₂, B₃, and B₄. The blades areindependently-movable and can be provided in the same plane. The bladescan be moved in the X and Y directions. The blades can be controlled toadjust, as needed, to expose a desired image on a substrate, and blockout the rest of the mask during exposure. For example, blades B₁-B₄ canbe programmed to allow exposure of only the uppermost alignment patterns12.

After transfer of the pertinent patterns, inspection of the positionthereof relative to other substrate features, such as alignmentreference mark 22, can take place to ascertain whether the latent imageof the alignment pattern is aligned within desired alignment tolerances.In a preferred embodiment, if the latent image of the alignment patternis aligned within desired tolerances, then the masking material 24 isexposed to processing conditions through a less obscured mask effectiveto transfer an integrated circuitry pattern onto the masking material.In the FIG. 9 example, such could comprise moving blades B₁-B₄ topositions which enable the integrated circuitry pattern borne by themask to be exposed. Subsequently, the masking material can be developed.In a preferred mask-blocking embodiment such as the one described above,the previously-blocked mask can be unblocked to provide a less obscuredmask wherein the less obscured and obscured masks comprise the samemask.

In another embodiment, after photoresist 24 is formed over substrate 16,the development properties of photoresist 24 are initially modified overalignment reference marks 22 and not any of the photoresist over dieareas 18. Inspection can then take place of the photoresist overalignment marks 22 to ascertain whether the development-modifiedphotoresist is aligned relative to alignment reference marks 22. In thisexample, modification of the development properties of the photoresistcomprises transferring, but not developing, an image of alignmentpattern 12 into the photoresist.

In yet another embodiment, the substrate is initially photoexposedthrough one of the set of alignment pattern openings and the circuitryopenings and not the other. Subsequent alignment processing can takeplace as described above and below.

Referring to FIG. 3, if the latent image or development-modifiedphotoresist is within desired alignment tolerances (illustrated in thisexample by a centered pattern 12 within pattern 22), mask 10 can furtherbe used to expose substrate 16 to lithographic processing conditionswhich are effective to transfer the integrated circuitry patternscorresponding to integrated circuitry openings within areas 14 onto themasking layer. This is illustrated in FIG. 3 in the form of crosshatching which occurs in die areas 18 where previously it had none. Inthis embodiment, the previous exposing of the substrate to form a latentimage does not expose any of the openings on the mask associated withthe integrated circuitry patterns. Accordingly, such constitutes afterthe first exposing of the substrate, second photoexposing the substratethrough the other of the openings on the photomask. In this specificexample, the first exposed openings comprise the alignment patternopenings 12 (FIG. 1).

In another embodiment, the mask 10 is not moved relative to thesubstrate between the first and second photoexposings. In this example,the position of alignment pattern 12 is analyzed intermediate the firstand second photoexposings.

In another embodiment, exposing of the masking layer comprises formingone or more latent images of only alignment patterns over the substrateand not any integrated circuitry patterns over the substrate. In theillustrated and preferred embodiment, the latent image of the alignmentpatterns and the underlying alignment pattern comprise box-in-boxalignment patterns. It is to be understood, however, that otheralignment patterns other than the illustrated box-in-box alignmentpatterns can be utilized.

Referring to FIG. 4, alignment pattern 12 is shown in a processing stepwhich is the same as that which is shown in FIG. 2. In this example,inspection of alignment pattern 12 relative to the underlying layer inwhich alignment reference mark 22 is disposed, indicates that alignmentpattern 12 is misaligned or is not aligned within desired tolerances.Such can be ascertained in this particular example because alignmentpattern 12 is not centered within alignment pattern 22. Where, as here,the latent image of alignment pattern 12 is not within the desiredalignment tolerances, the relative positioning of the mask and thesubstrate can be changed or corrected to within desired tolerances. In apreferred embodiment, the substrate can be moved relative to the mask,as by moving a wafer stage upon which a wafer or substrate is received.In the preferred embodiment, the correction for mask misalignment takesplace prior to transfer of any of the integrated circuitry patterns.Although FIG. 4 shows a translation error resulting in a misalignment,other alignment errors can be processed in accordance with variousaspects of the invention. For example, alignment errors stemming fromrotational displacement, magnification errors, trapezoidal errors,and/or distortion can all be addressed by various embodiments of theinvention.

In one embodiment, if the latent image is not aligned within desiredalignment tolerances, an alignment correction is calculated. Thecalculated alignment correction can take into account alignment errorsstemming from not only translational errors, but also rotationaldisplacement, magnification errors, trapezoidal errors, and/ordistortion. After calculating the alignment correction, the relativepositions of the mask and substrate are corrected prior to reexposingthe substrate to transfer the integrated circuitry patterns. In apreferred embodiment, correction of the relative positions of the maskand substrate is effectuated by moving the substrate relative to themask. Such is illustrated in FIG. 5. There, the cross hatched areas overdie areas 18 correspond to transferred integrated circuitry patternswhich have been transferred from a position-corrected substrate. Theoriginal misaligned position of alignment pattern 12 is shown encircledby a dashed line at 26. The subsequent corrected position of alignmentpattern 12 is shown encircled by a dashed line at 28. The photoresist isreexposed to processing conditions through the mask effective to formimages defined by the mask which are received over the wafer.

Referring to FIG. 6, a flow diagram of certain methodical aspects of theinvention is set forth generally at 30. The illustrated method comprisesusing a latent image of an alignment pattern which is received by anundeveloped masking material layer to ascertain whether the latent imageof the alignment pattern is aligned relative to a substrate over whichit is received.

In a preferred embodiment, the position of the latent image isinspected, at 32, relative to an underlying substrate layer. In apreferred embodiment, the underlying substrate layer comprises analignment pattern relative to which the latent image is inspected.Alignment of the latent image is ascertained, at 34, relative to theunderlying layer. At 36, if the latent image is misaligned, an alignmentcorrection is calculated and implemented to correct the misalignedimage. In a preferred embodiment, implementation of the alignmentcorrection comprises moving or repositioning the substrate relative tothe mask.

Various methods of the invention can be implemented by a computer havinga computer-readable medium on which are stored instructions which, whenexecuted by the computer, implement one or more embodiments of theabove-described invention.

Referring to FIGS. 7 and 8, and in accordance with one embodiment of theinvention, a semiconductor wafer alignment tool is shown generally at 38(FIG. 8) and comprises an image-forming apparatus 40, an inspectionapparatus 42, an adjustment apparatus 44, and a correction processor 46.

Image-forming apparatus 40 is configured to form a latent image of analignment pattern which is receivable by a masking layer over asubstrate. An inspection apparatus 44 is operably coupled withimage-forming apparatus 40, and is configured to enable inspection ofthe position of the latent image of the alignment pattern relative to anunderlying layer of material over the substrate. The inspectionapparatus can also ascertain whether the latent image is aligned ormisaligned relative to the underlying layer. In a preferred embodiment,adjustment apparatus 44 is operably coupled with the image-formingapparatus and is configured to make image alignment adjustments relativeto a misalignment of the latent image. In a further preferredembodiment, correction processor 46 is operably coupled with theadjustment apparatus 44, inspection apparatus 42, and image-formingapparatus 40, and is configured to calculate an image adjustment andprovide the calculated image adjustment to the adjustment apparatus 44for operation thereon. One or more of the above-described apparatus, orcomponents thereof comprising the alignment tool 38 can be implementedin any suitable hardware, software, or firmware.

In but one embodiment, semiconductor wafer alignment tool 38 cancomprise a programmable computer, such as the one shown generally at 48in FIG. 7. Computer 48 can be used or programmed to implement thevarious methods of the invention. Computer 48 can include a hard drive50, an input device 52, and an output device 54. Hard drive 50 generallyincludes a central processing unit (CPU) and a memory system thatcommunicate through a bus structure. The CPU includes an arithmeticlogic unit (ALU) for performing computations, various registers fortemporary storage of data and instructions, and a control unit forcontrolling the operation of the computer in response to instructions toa computer program such as an application or an operating system.

The memory system generally includes a high-speed main memory in theform of a medium such as a random-access memory (RAM) and read-onlymemory (ROM) semiconductor devices and secondary storage in the form ofa medium such as floppy disks, hard disks, 56, tape, CD-ROM, etc. andother devices that use optical or magnetic recording material. Thememory system stores programs such as a computer's operating system andcurrently running application programs, e.g. such as those whichimplement one or more of the inventive methods described above. The mainmemory also includes a video display memory for displaying imagesthrough a display output such as monitor 54. Input device 52 and outputdevice 54 are typically peripheral devices connected by bus structure tothe computer. Input device may be a keyboard as indicated, but may alsobe a modem, pointing device, pen, or other device for providing inputdata to the computer. The input device can also include various opticalscanning devices which are capable of examining the alignment patternsin measuring the desired parameters described above. An exemplary deviceis a so-called stepper. An output device 54 may be a monitor asindicated, but may also be a printer, modem, sound device or otherdevice for providing output data from the computer. The input and outputdevices may be combined into a single device if desired.

The various invented methods and apparatus can be used to process onewafer per lot, multiple wafers per lot, every wafer in a lot, or everymasking field on a wafer. Advantages of the present methods andapparatus include real time correction of image misalignment which canreduce processing time thereby increasing wafer throughput. Otheradvantages include tighter alignment tolerances which can be achievedwith system-corrected alignment. In addition, system-corrected alignmentcan reduce alignment errors by further removing the human factor fromthe alignment process. Hence, wafer rework can be reduced through theerror reductions provided by the present invention.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A semiconductor wafer alignment tool comprising:an image-forming apparatus configured to form a latent image of analignment pattern receivable by a masking layer over a substrate; and aninspection apparatus operably coupled with the image forming apparatusand configured to enable inspection of the position of the latent imageof the alignment pattern relative to an underlying layer of materialover the substrate and ascertain whether the latent image is alignedrelative to the underlying layer.
 2. The semiconductor wafer alignmenttool of claim 1 further comprising an adjustment apparatus operablycoupled with the image-forming apparatus and configured to make imagealignment adjustments responsive to a misalignment of the latent image.3. The semiconductor wafer alignment tool of claim 2 further comprisinga correction processor operably coupled with the adjustment apparatusand the inspection apparatus and configured to calculate an imageadjustment and provide said calculated image adjustment to theadjustment apparatus for operation thereon.
 4. A semiconductor waferalignment tool comprising: an image-forming apparatus configured to forma latent image of one set or another of alignment patterns and circuitrypatterns formed on a photomask, the latent image receivable by a maskinglayer over a substrate; and an inspection apparatus operably coupledwith the image forming apparatus and configured to enable inspection ofthe position of the latent image of the alignment pattern relative to anunderlying layer of material over the substrate and ascertain whetherthe latent image is aligned relative to the underlying layer.
 5. Thesemiconductor wafer alignment tool of claim 4 further comprising anadjustment apparatus operably coupled with the image-forming apparatus,the adjustment apparatus configured to make image alignment adjustmentsresponsive to a misalignment of the latent image.
 6. The semiconductorwafer alignment tool of claim 5, wherein the adjustment apparatus isconfigured to reposition the substrate and/or the photomask to make theimage alignment adjustments responsive to a misalignment of the latentimage.
 7. The semiconductor wafer alignment tool of claim 4 furthercomprising a correction processor operably coupled with the adjustmentapparatus and the inspection apparatus, the correction processorconfigured to calculate an image adjustment and provide said calculatedimage adjustment to the adjustment apparatus for operation thereon. 8.The semiconductor wafer alignment tool of claim 4, wherein theimage-forming apparatus is configured to form at least two latent imagesof the set of alignment patterns, and wherein the inspection apparatusis configured to ascertain whether the latent images of the alignmentpatterns are aligned in X and Y directions.
 9. The semiconductor waferalignment tool of claim 1, wherein the image-forming apparatus isconfigured to form latent images of at least two alignment patterns, andwherein the inspection apparatus is configured to ascertain whether thelatent images of the alignment patterns are aligned in X and Ydirections.